Optimizing rate of nitrogen for corn - how good can it be?

Transcription

1 Optimizing rate of nitrogen for corn - how good can it be? James J. Camberato jcambera@purdue.edu

2 Objective of better N management Choose a combination of source, placement, timing, and rate of N application that minimizes the amount of unused N and its susceptibility to loss while optimizing profit

3 Indiana corn production 6 million acres 90% grown in rotation with soybean 50% anhydrous ammonia, 40% urea-ammonium nitrate solution, 10% granular urea Less than 25% of the N is applied in the fall (AA) mostly in the northern half of the state

4 Indiana precipitation equal or lesser to Iowa during the growing season Indiana has greater prec. than Iowa in the off-season vs 11-14

5 Indiana soils vary a lot ~210 lb N/ac ~ lb N/ac

6 Thanks John Sawyer!

7 Experimentally-derived N rate recommendations replaced yield-based N recommendations R I D E Yield-based Experimentally-derived Other

8 Indiana - no/weak relationship between N fertilizer needed and yield achieved 250 site-years

9 Yield-based N rec. for corn was suggested first in 1966 (G. Stanford, USDA-Beltsville, Md.) Fertilizer N recommendation = (Yield x N factor at harvest - soil N contributed) / efficiency of fertilizer use

10 Comparison of MRTN to a mechanistic model N recommendation across 22 Indiana C/S locations

11 Predictions needed for an accurate yieldbased N recommendation Accurate prediction of: Crop yield Plant N content associated with crop yield Soil N mineralized Fertilizer lost (efficiency of fertilizer use)

12 Variation in yield 113 bu/acre ACRE 136 lb N/acre P34A20, 33K site-years

13 Yield range per field over 5 corn years in C/S rotation 29*

14 An example of modeled yield vs achieved yield at ACRE and PPAC Across 33 site-years of data at ACRE and PPAC maximum yield was predicted at 201 bu/acre vs actual yield of 204 bu/acre

15 Crop N requirement Based on expected yield x the concentration of N in the above-ground plant at physiological maturity (expressed on a bushel of grain basis)

16 Stanford, N factor Yield target (bu/ac) x plant N concentration (1.2 lb N/bu) Based on experiments conducted from 1946 through 1960 in GA, MS 3 years each; NE 4 and 2 years at 2 locations

17 Regional N management project Nitrogen rates 0 to 280 lb N ac -1 in 40 lb N ac -1 increments, all at planting or 40 lb N ac -1 at-planting and the remainder at V9. Hybrids Several used based on location 16 locations across 8 states Support from:

18 Corn is less efficient at higher N rates in producing grain per unit of N content Shafer, 2016

19 Determine EONR for each location EONR Shafer, 2016

20 Efficiency at the optimum is key Shafer, 2016

21 Variation in across 30 sites resulted in ~90 lb N/a range in plant N Bushel lbs. N per Yield Plant N at per lbs. N bushel Goal harvest Least effic Most effic Avg Shafer, 2016

22 was related to plant N content at VT when no fertilizer was applied soil N supplying capacity Shafer, 2016

23 Variation in crop N requirement Assuming yield is predictable, IE can vary enough to cause meaningful difference in crop N requirement Variation in IE was related to soil N supplying capacity, but not EONR, Yield@EONR, soil OM, or most indices of adequate and well-distributed rainfall

24 Mineralization of soil N Soil N microbial release of N from soil organic matter, microbial biomass, and crop residues. Perhaps release of ammonium (NH 4+ ) form the interlayer of 2:1 clay minerals Soil N can contribute a significant portion of the N accumulated by the crop in some soils Substantial differences can arise from year to year in soil N contribution

25 Grain yield without fertilizer N 101 Indiana trials, corn after soybean Grain yield without fertilizer N

26 Nitrogen mineralization Field - N uptake by corn fertilized with ~25 lb N/acre as 2x2 starter was used to assess soil N mineralization in 2015 season Laboratory - N mineralization potential was determined under temp. and moisture conditions for expt. areas at 6 locations after 10 years of corn/soybean rotation ACRE

27 Total plant N at R6 (lb acre -1 ) Field 81 evaluation Crop N content at maturity with starteronly O.M. 4.0% 3.6% 2.9% 4.1% 2.8% 2.7% Moser, 2016

28 Total inorganic N (mg kg -1 ) Laboratory incubation N release after 50 days under ideal temp. and moisture O.M. 4.0% 3.6% 2.9% 4.1% 2.8% 2.7% Moser, 2016

29 Field Laboratory Moser, 2016

30 Mineralized N (mg/kg) Field cap. * Nitrogen mineralization decreases above and below field capacity kpa 10 kpa 10 0 Idaho Silt Loam Adapted from Stanford and Epstein (1974) Soil Water (g/g)

31 Starter-only grain yield, bu/acre Yields with starteronly were greater in soils with better internal drainage Location Ksat (μm s -1 ) Moser, 2016

32 Starter-only Yield grain (kg/ha) yield, bu/acre Yield and Excess Water R² = 0.83 DPAC ACRE TPAC Ksat (μm/s) R² = R² = Excess Water (mm) Moser, 2016

33 Starter-only grain yield, bu/acre Yield (kg/ha) Yield and Excess Water SEPAC PPAC NEPAC Ksat (μm/s) Excess Water (mm) Moser, 2016

34 Summary Yield-goal based and model-driven N recommendation systems attempt to estimate N requirement by predicting (yield per acre x total plant N content per bushel of grain anticipated minus soil N) / an efficiency factor

35 Yield The range in yield from an available N recommendation model varied 50 bu/acre, sometimes high sometimes low All other things being equal the N requirement based on yield can vary by approximately 50 lb N/acre

36 Nitrogen content per bushel Assuming yield is predicted accurately and all other things are equal Variation in plant N content per bushel at the optimum N rate can vary as much as ~0.45 lb N per bushel which would result in a 90 lb N per acre variation in plant N content at a yield of 200 bu per acre

37 Soil N mineralization Soil N mineralization can provide little to all of the N accumulated by the crop at physiological maturity In a particular field year-to-year variability ranged from 40 to 100 lb N acre -1

38 Conclusion Variation in currently difficult to predict factors suggest that static yield-goal based N recommendations systems can at best estimate fertilizer N requirement no better than lb N/acre in Indiana systems which is no better than experimentally-derived N recommendations Models should be thoroughly tested with existing data to evaluate whether or not they can do better

39 Questions?